The field of RFID systems has evolved over the past years from systems developed in relatively large packages (size of a cigarette package) containing battery powered transmission/receiving circuitry or transponder, such as the identification system disclosed in U.S. Pat. No. 4,274,083, to passive systems (the size of a credit card) in which the transponder receives its power from the base station or interrogator, such as the identification system disclosed in U.S. Pat. No. 4,654,658.
Although, an inexpensive low-power RFID system having a battery powered transponder allows for greater distance between the interrogator and the transponder units, the physical size of the transponder unit has pushed the industry towards the passive transponder technology as disclosed in U.S. Pat. Nos. 4,654,658 and 4,730,188. However, the limit in RF communication distance between transponder an interrogator in passive systems is in the 2 foot or less range if reasonable accuracy of information collected is to be achieved.
U.S. Pat. No. 4,724,427 discloses a passive RFID transponder as well as a hybrid battery operated version which addresses both types of RFID systems.
The memory used in RFID systems depends on the type of system used wherein, most passive systems use a programmable read only memory (PROM) of some sort that will retain its programmed data even when power is disrupted or removed while a battery packed system may use any memory type, including random access memory (RAM), that requires a continuous power source to retain programmed data.
It is most desirable to use battery based transponder systems to gain communication range between the transponder and interrogator. If the battery is rechargeable, so much more the better. The present invention discloses various methods to recharge battery cell(s) of battery backed electronic systems and more particularly to recharge an RFID transponder's secondary cell(s) that may be situated in a remote location. Also, all U.S. patents cited herein are hereby incorporated by reference.